In her US citizenship application, application to another permanent residency in a different country may bring some questions. It may not be an issue, or it may be. Especially if she moves to Canada to live with you during this stage, she can even lose her green card if she crosses the US border and reveals she has no longer intend to live in the US permanently. While crossing the US border, the agent will ask the purpose of the trip in Canada, and if the agent figures it out she is indeed living in Canada and got a permanent card over there, she can try to confiscate her green card. In order to apply to US citizenship, a person needs to stay 3 months at the same location she is applying, she can apply certain months before completing 5 years residency in the US though. But she better stays at that location while waiting for the interview date for the citizenship for the US.
Once she got the citizenship of the US, she can sponsor you to the US if you guys care to live there, much easily.
Besides all these points, sponsoring her to Canada will take time even if you guys already started to "import" her to Canada. So she may have to commute to you during this time or you may also consider living in the US for a while.
Another issue is, if you guys bother or not; the moment she married with you, she has a significant tie to Canada, if she has bank accounts, credit cards from Canada as well, and she actually stays in Canada more 186 days; that triggers very likely if not certainly, she needs to pay taxes to Canada even if the earning is from the US. On the other side of the border, she has to fill out US tax return as a resident as long as she has a green card or citizenship.
My suggestion is to apply her Canadian perm residency after she gets the citizenship, and you guys need to find a solution what to do during this year in terms seeing/living each other. Marrying her or not during this time is not a very big issue. However, when she visits you, Canadian border agents will be suspicious that she may not actually go back to US, since her visit is supposed to be touristic and short term. But having a husband in Canada can defeat the claim she is only short term visitor. Same thing happens when you visit her in the US.
