Just some very general advise, obviously I don't know you or your situation in any personal manner. However, generally speaking I would think it would probably just be easier for your girlfriend to move to Texas, for you to marry, and for you to sponsor her for a Green Card.
Spousal sponsorship tends to be faster in the States, though not always but usually its faster. Further, I really think you should go to Canada first before you decide to quit your job and move up there. See if you even like it and can get a job.
Do you realize Texas has a much better economy than Ontario? Things in Texas are cheaper, Canada is very liberal with very high taxes to fund all sorts of socialist programs, plus are you sure you can adjust to the brutal winter climate?
Don't get me wrong, moving up to Ontario might be the best thing for you, I don't know. However just from what you said it kind of sounds like you are not ready for a big move like that, since you've never even been out of the states.
Canada seems to be great for people from Asia, Europe, Africa etc.. but I don't think most Americans (or anyone who has lived in the States) would really like it up here or could live here permanently, just my honest humble opinion.
I know it's a matter of opinion but thought I'd give mine too when it comes to people living in the US not liking Ontario. I've been living in the US for the past 11 years and am getting ready to move to Ontario and I just can't wait! I've been to Canada, Ontario most specifically, a multitute of times and I love it there and I plan on leaving the US permanently for Canada in a few months. Also, spousal sponsorship is not faster in the US and I don't agree with the economy statement either.
My advice would be for you to do your own research. I'm assuming you are American if you've never traveled outside the US...how about visiting your girlfriend? take a few trips to canada and see for yourself what Ontario has to offer. I've been in a long distance relationship myself for close to 3 years now and I know how frustrating it can be...you need to get moving on your immigration paperwork...it takes a while to get anything. Good luck again.