Hello all, I just wanted to share my experience as a guidance.
My wife is sponsoring me, she lives in Quebec, I am from a non-exempt visa country (El Salvador) and I'm on a student visa in the US. I've had 4 TRV since I have family in Québec City and I have visited many times.
I got married in Canada on 2009, and my TRV Visa expired on October 2010, I went one last time to apply for a TRV and in all documents I stated I was married to a Canadian Citizen, maybe because they saw my travel history I was granted another TRV that was good until May 2011, during all that time I've been traveling maybe once a month or 2 months and never had any problems at the border, always telling the truth, I was going to visit my wife in Québec.
We started the PR process and the application was received on April 15 since we did it ourselves and even with the application in process I never had any problems visiting my wife, now since I work here in the States I can't stay for extended periods of times, I used to travel for holiday weekends, and the longest stay I had was 1 month, now I'm hoping the whole process will be done before the year ends so I can have a smooth transition.
But to answer the question, as some people have said before it always depends of the Immigration Officer at the border, but if you tell the truth and probe you are going back you should be fine, I never had any issues going back and forth, I visited maybe 12 or 13 times in a period of 1 year and a half.
Hope it helps, have a good day all!