I am planning a tour across Michigan's Upper Peninsula next summer. About 30-40% of the roads will be backroads and single track.

I have looked at some off-road touring bikes such as the Surly ECR and Salsa Fargo. Any other recommendations for a suitable touring rig for this adventure?

I went with the Trek 1120 for offroad touring. I like the proprietary racks, among other features. I looked at the Surly and Salsa offerings, but they didn't have visual appeal.

Just looked up the 1120. Thats an interesting bike.
The proprietary racks are neat, except they will most likely be obsolete once trek discontinues them in a couple years, but if they last the who cares about that.

Lots of mounting on the fork and frame, the handlebar bag rack gets the bag away from cables, solid gearing range, and its really creative with the chainstay design and adjustable chainstay length.

I usually dismiss Trek's offerings as trendy and not designed for the long term, but there is so much creative implementation here it almost gets me to want to think they did a good job.
Almost.

If you're genuinely interested in the 1120, consider waiting for REI to release their ADV 4.2 (look it up). There will likely be a 15% off coupon in May.

Have you considered a used bike or building up a frame? I have wanted an ECR since they came out, but not in budget. I have a Soma Wolverine that I really like for dirt road touring and have ridden a little singletrack too. Mine has 2 sets of wheels, a 700c with 700x40 and a 26” with 26x2 shaved Rocket Rons. The 2” tires are great for everything but sand and a low BB is something to consider depending on the type of trail. I only hit a pedal one time when i was riding agressively and in very uneven ground. The frame will take 700c x 50 also.
My other dirt tourer in a 1984 Schwinn Mirada step though that has WTB Ranger 26x2.8 tires. I have maybe $200 into this bike and $100 was tires. It is great for dirt roads, singletrack that is not rough, and rough paved roads. It is not a traditional choice, but I am all about function and it rides great.
Lots of options in a used bike. For a new one, a bikepacking rig work work well.
Enjoy the trip and watch out for the black flies in the UP. They are worse than mosquitoes.
Tom Palmer
Twin Lake, MI

I have experience touring in the North Woods, including a 250 mile loop in the Chequamegon NF in early September. For that trip I rode my Salsa Mukluk with 3.8" Jumbo Jim tires and Jones Loop Bars. It would be hard to find a better setup for rocky and sandy forest roads and ATV trails, especially in Bayfield county. I have a trip planned to ride across the UP from Sault Set. Marie to Ironwood and will use the fat bike because I want to ride some shoreline west of Whitefish Point as part of the trip, and know that some of the roads will be sandy/soft. I also plan to ride across the Superior NF in northern MN from Hovland to Crane Lake and plan to ride my Salsa Fargo. I have a 2012 Fargo setup with a 3" front tire and an Ardent 2.4" on back for this kind of riding. The Fargo is my favorite bike and I have about 12,000 miles on it; most frequently it is set up with Nanoraptors for gravel road exploring. I have been giving thought to building the perfect North Woods touring bike and think that maybe it would be a new Fargo set up 29"+, although the right fat bike setup would be a close second, and with a second 29+ wheel set hard to beat. I think an ECR setup with Jones Loop Bars would be right there as well.

Tech rocky singletrack? Sand? Beach? Need front sus? Frame bags or racks? I use a Karate Monkey with 29 x 3 " tires, tough to beat that set up for versatility, also a rigid front fork. They make some sort of slick tires in the 2.5 to 3" x 29 " tires. Got some on the ground reports for what kind of tires are best suited for that ride?

Love my ECR. Worth every penny. Goes anywhere. Comfy. Full of confidence. Works really nice loaded or unloaded.

Do you want to use racks or not? How much weight are you carrying?

I see a lot of unnecessary slowness (suffering) if only %30 is say, well groomed dirt roads.

I'd go for something like a gravel bike similar to a Cross Check or Haanjo EXP.

And bring a shotgun for the mosquitos.

Thanks for the suggestion. Nice review here in BikePacking.com:
The New 2018 Trek 1120, a Bikepacking Stache - BIKEPACKING.com

I grew up in the UP, so I know that the black flies can be horrendous! It is great to hear about your experience with the Wolverine. I saw one for sale locally on CL, but I was a little unsure whether it could handle dirt road touring. My plan B is to build up my 94' Jamis Mountain Bike for touring. It has a great frame (Tange infinity), but the geometry may not be the best for a long tour. Thanks for your advice!

I am considering a similar route. May dip a little farther south on the east end of the UP. The UP has a lot of sandy roads, so bigger tires would help. Thanks for sharing your advice!

I expect that some of the roads will be sandy, but not planning much technical, single track. Thinking rigid fork with frame bags right now. The Karate Monkey sounds like another good option.

^^^^ Mine is older with the 29er set up. New ones are 27.5 plus. I've been looking at the vee rubber tires in 29 x2.8. I have also used Geax Tattoos in 29 x 2.3 with a 35 mm rim. Slick with some siping and inverse tread. At 6' 4" 29ers fit me well. As said a 29 or 27.5 x 3" tires gives you lots of options. Can also run say a 2.3 - 2.5 as needed.

Not a fan of the 1120. All I can see that they did with the downtube was take away space for a larger frame bag. And the racks? No thanks. One of the reasons bikepacking makes sense to me is that you attach bags directly to the frame, so fewer failure points. These racks just reintroduce possible failure points.

Chacun ses gout, but it's certainly not for me. I'll take a Troll or Ogre and pocket the $1,500.