She's planning on going to University in MN for 3 years and I'd like to live with her while she's studying. If not I guess I'll have to keep it down to 'visits' every now and again. It will be difficult for her to afford to visit me while she's studying.
First up with regards to the VWP. If you leave the US by land border into Canada within the 90 days the VWP is valid they will not remove your VWP, you can go backwards and forwards BY LAND between the US and Canada multiple times within the 90 day limit.
When I lived in Canada I used to go down over the border all the time to the US on trips and shopping etc. I probably had 3 VWP cards within a year. There is as they say no rule of thumb. If the border guard can see you are a resident of Canada (even if not a citizen) and pop down to the US for 1 week periods, or long weekends they can usually ascertain that you are a legit traveller. However this is not guarented but I personally never had any problems and neither did my work mates. Things however may have changed since then.
Your best bet providing you are under 30 is to get a BUNAC for Canada. You can reside in Canada for a year with this and you have a work visa that allows you to apply for any kind of job. If I where you I would get the BUNAC and live in Canada and pop down for long weekends/weeks. Just worth noting that in Canada the basic holiday rate unlike the UK is usually 5 days a year in your first year. Not great is it?
I dunno where she lives in MN but if she is near the border you could live on the other side, that would cut your costs massively. Once you have the BUNAC if you land a really good job in Canada you can probably have your employers sponsor you a visa. I know a few people who did this.
Realistically though the nearest area to the MN border in Thunderbay and it's not exactly Toronto, Ottawa or Montreal when it comes to jobs.
If you are loaded then maybe you could cough up and go to Uni in the US, but I know that is not an option for 99% of people

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You might want to sit and discuss the options with her and see if she fancies going to Uni in the UK or elsewhere in Europe, or even Canada.
Sorry mate this sucks, I know all too well.
TomPaine