I am far from an expert but I have fished both north of Fargo (Oslo, Drayton) and Lockport, Manitoba. It was in 2008 and 2009. The first year we went to Oslo and did poorly the first two days and Drayton the 3rd day. We did OK at Drayton with the biggest cat being about 19lbs. I also caught a 7 lb walleye.
The next year we went with Cats on the Red up near Lockport, Manitoba. We used a guide since we had never been there before. It was my first time using a guide and it was a good trip. It was slow by their standards and hot (85F in September). My brother and I caught about 65 cats in two days up to more than 30 lbs. We went off shore after getting done with the guide for the day and caught a 25 lb cat just messing around. The last morning we went off shore for about an hour before heading back to the states and caught a 12 lb'er. I was stunned when I weighed it at 12 lbs since it looked so small compared to what were had been catching. I thought it was going to be 5 or 6 lbs.
Generally, the farther north you go the better the fishing. It has been a while since I checked the forums for info up there but when I was researching it anglers tried to catch 1 ton of catfish per day when they were really slamming. I have always meant to go back but have not gotten there since, but I would like to.