Yum! First time having poutine and it was delicious! We ordered two larges that was enough to share for 3 people. I would recommend getting two dishes that are completely different from each other because they tend to start tasting the same after awhile! You may want to get a coke or some kind of soda to wash down all that fat that you're eating... delicious fat though! We just had water and while it helped, I don't think it did the job.
I can't remember which two poutines we had, but I'd say any one of them are good. We got the regular/traditional one and one that had all this meat. The meat one was a bit overbearing because the sausages were huge and very filling. I'd recommend something lighter if you're small like I am and you're sharing just to try it for the first time.
Definitely get here early because a line sure does build up quickly! We parked on the streets in the neighborhood ... not sure where else to park!