sun CR18 700c wheels and Schwalbe Marathon plus?
 

Is this a good match? I got the rims already to go but waiting on the tires, I throw an old set of tires I had on the rims to try them and it was a struggle to get the tires on. after 15 minutes I had to use tires levers to get the tires on.

Is this common with sun rims or just the combo I tried?

The old set of tires are Continental Ultra sport 700x25c. The schwalbes I want to order are 700x 32

I installed these tires on an Alex rim last year and found the same issue you did. It is a common complaint with the Schwalbe. Actually.. somehow... I managed to tear the rubber covering on the wire bead on one of the tires. So I would urge you to make sure the tire is seated correctly before you bring it to full pressure.

I had 2 Marathons and got one flat in over a year of service. For some reason, changing the tube on the road wasn't that hard. Must have "broken in". The other tire is on the rear of my Bianchi Volpe and hasn't had a flat in about 3000 miles.