visajourney.com has all the free info you need on relationship visas
http://www.visajourney.com/content/compare Read the
k1 (fiance visa--not married) and the CR-1 (married) and decide which is best for your situation. K1 is fastest (if their is such a thing with immigration,lol) BUT you can not work. CR-1 takes a bit longer, have ur greencard from the start, can work from the start and travel out of the USA from the onstart! and it is cheaper--just the biggest drawback is it takes a few months longer
During the visa process one can visit the usa. many do with no problems. i flew to DC monthly from nova scotia. and yes some do get denied entry, but thasts because most are not prepared. all comes down to the poe officer. ensure one has ties to canada--aprtment/house lease, return airfare, etc etc, anything to help proove ur case that u will be returning. my advice:
Canadians Visiting the USA while undergoing the visa process, my free advice:
1) Always tell the TRUTH. never lie to the POE officer
2) Be confident in ur replies
3) keep ur response short and to the point, don't tell ur life story!!
4) look the POE officer in the eye when speaking to them. They are looking for people lieing and have been trained to find them!
5) Pack light! No job resumes with you
6) Bring ties to Canada (letter from employer when ur expected back at work, lease, etc etc)
7) Always be polite, being rude isn't going to get ya anywhere, and could make things worse!!

Have a plan in case u do get denied (be polite) It wont harm ur visa application if ur denied,that is if ur polite and didn't lie! Refer to #1
and you may read of cases where one visits the USA and then just stays! And what they do then is AOS (Adjust of status) and that is perfectly legal IF you had no intentions of doing that. Just out of the blue you decided to stay! It is a much faster way to obtain the greencard, but one can't leave the USA or work until you get the greencard! And to travel out of the USA before the Greencard, once would have to get advance parole (AP), but we are talking months, like 2-3, so its not that long! But keep in mind, one has to have NO intentions. How do they prove it, by sticking to ones story,lol, thats all i'm saying about that.
I went the Cr-1 route back in 2004. Paperwork is easy enough--al the info is on VJ, the waiting is the hardest part, but it is getting easier, more and more of the paperwork is being completed online! Some ifo you wil require is your long form birth cert (has parents info right on the card) Cdn police background check---1 wil do, as it covers all of canada (USA citizen does not need 1) if you have ever had a criminal record, wil need fingerprints as well. NO criminal record = no fingerprinting. any divorce paperwork if appl. check out VJ, lots of free info. cheers