I've heard the pie is good so I will definitely get a piece, maybe two.
From St Mary I'll probably just head towards Browning and Cut Bank
Wateron Village is a nice place for a day off. Was there again in '09. The ride there from St. Mary is nice, but difficult once you hit Chief Mountain Hguhway. Worth it if you have the time. However, I think indoor lodging can be difficult if you are not campimg. I also don't know what's available lodging wise around Magrath before you head back into the U.S. at Del Bonito. That's a neat but lonely ride. There was nothing between Magrath and Cut Bank except for a store in Del Bonito, before you cross the border. IIRC, it is some 70 miles to Cut Bank. Maybe it's been built up more since I rode that stretch in '99.
St. Mary to Browning via U.S. 89 starts with a 5-6 mile climb then a bunch of ups and downs. Cutting off at Starr School Rd. to Browning may be easier. If you are a glutton for punishment and have the time, take U.S. 89 and then MT 49 to East Glacier to pick up U.S. 2 to Cut Bank. MT 49, also known as Looking Glass Hill, has some pretty views, including one fo Lower Two Medicine Lake. Some climbing is involved, but it's not overly difficult, and there is a nice descent to E. Glacier, where you will find a couple of places to et and get snacks and drinks. There is also at least one motel/campground there. IIRC, it's 32 miles to East Glacier if you go that way. Total of 80 miles to Cut Bank.