Hey! I was doing that journey from Washington to BC. I know the pain of being so close yet so far. I got a student visa and that gave me legal standing within Canada, yet at the time, we did outland since it was 'faster' I'm telling you now. DON'T DO OUTLAND. they now have the same processing time of 1 year. whereas before it was ~5 months outland vs 26 months inland. Now they're both a year but inland gives you Open work permit. Which I wish I had right now. If you're able to. get some legal standing in Canada. extended visitor. what ever it may be.
the only thing that might be bad about that is that if you're not already married.. it might be viewed negatively getting an extended visa then getting married. But the border agents don't have to know about that. but know how to word around it if you're asked.
you can do common-law as well, but you have live together for one year before you can apply. We did this since we didn't want to take the romance out of proposing as well as having more proof for our relationship.