Before you actually apply, border officials tend to always ask a lot of questions about what your plans are, who will be moving where, what your jobs are in your respective countries, and how long you will be staying in the country you're entering. Once you say you apply, they know you're serious and tend you let you through more easily.
Technically, your wife has 6 months in Canada before she has to leave. If you want to stay longer than this, you can get a visitor record. Or get a temporary resident visa. If your wife goes home to visit family for a week or so and then goes back to Canada, when she re-enters, if she is let in, she would get another 6 months. Each visit is independent of each (confirmed in a call to CBSA).
When your wife enters Canada, the border officials will always ask how long her visit will be. If she says, "I don't know", that she quit her job, and she is just going to live with you, she might be denied entry. Border guards want to know that you have a plan. Because let's say that your application is not approved, they'll think she might then live in Canada illegally, that she won't go back. They want to know that your wife still has ties back in the US. Don't show up with all her stuff, planning to permanently move and expect to be let in.
Always know when she will be going back to the US. I think that's the most important thing.