This looks like it will be a huge headache...
It is. (I just did this for my husband who was here in F-1 status and now has a green card...)
Your main problem is that neither of you are US citizens or permanent residents.
What does this mean?
You get an F-1 student visa for law school, she is not your wife, therefore she is no one and has no right to follow you to the US, much less work there.
You get married, you an F-1 student visa, she gets an F-2 visa (a dependent of someone on an F-1 visa), which means she can follow you, but in that status, she can neither study nor work. (IE To go to med school, she'd have to petition a change of status to F-1 for herself, having a med school acceptance in hand).
Neither of these options is very pretty.
Problems I see with the Fiancee thing:
Only US citizens are allowed to petition visas for Fiances. That's not you, so you're SOL. (IE If you want her to come to the US because of you, she MUST be your wife.)
Furthermore, the problems I see with the Uncle thing:
If she gets an H-1 visa to work with her Uncle, and then STOPS working there, her visa expires and she has to go back home. So the H-1 from the Uncle is most likely NOT going to solve your problems. (Of course, you could have here work there while she's applying to Med School, etc, but she couldn't stop working there until her change to F-1 comes through.)
That said, there is another loop-hole, IF you can find a way to exploit it.
The rules of the F-1 student visa say that, upon GRADUATION from a program, a student can petition employment for up to 1 year. This is called OPT.
The easiest way to exploit this loophole is usually to come to the US, enroll in an English school as an F-1 student, graduate (the programs often take as little as 6 months), and then take your year of OPT.
Your problem? You're Canadian. You already speak English. No one is going to give you (or your girlfriend) an F-1 visa to study English.
Bottom line: she can either marry you, and follow you as an F-2, or you can just spend the year apart while she does the med school app thing.
Either way, you'll probably end up separated anyhow. You never know where you'll get in for law school, nor where she'll get in for med school...
Good luck, and let me know if you have any further questions...