The post of what I did is somewhere here as well but I can give the short version again...
You are attempting to use the "dual-intent" rule that CIC has. Basically she has the intent to immigrate and is in the process of that application...and at the same time she has the intent to visit for a short term visit and return. So two intents!
The important thing for you now is that the Visitor Visa is processed as a TEMPORARY VISA. Remember this above all else. It is the most important thing they consider...WILL SHE GO HOME AT THE END OF IT?
My approach was:
In the invite letter I mentioned the spousal application and even gave the case number. They know who you are so you might as well make it easy for them and tell them that right from the start.
I gave the reasons for her visit as the real ones. To visit and stay with me, to meet my family, and even look around at neighborhoods, places to live, and schools. Don't try to make it seem like a simple visit...they will see through that... be honest and just say it like it is. And if they think the reasons to visit are not important enough they can deny the visa because the reasons are frivalous and not worth the risk of her overstaying.
Do not say anything that will make them thing it is PERMENENT move. She is visiting. She is NOT bringing things with her to leave here. She is NOT bringing a load of belongings to make the move easier later. She is NOT looking for a job. Nothing permanent.
The important thing is to give reasons why she will return. Job at home... school at home... property... child at home. Whatever helps that.
And you have one very good reason to return...be sure to use it... "She has to return home in case of an interview or if any other communications or documentation is needed to complete the outland spousal sponsorship." I mentioned this to show that we understand the process we are in and can at least explain why she has to be back home to follow that process.
So three simple things...
1. Good reason to visit.
2. Nothing showing a permenent move.
3. Good reason to return home.
And remember... you have already bared you life to them to get the perm visa... so don't start being shy now.