Thank you for your response

...What if they don't ask if I plan to sponsor, and they simply say how long do you plan to stay in Canada, what are you coming here for, etc.? Can I say that I plan on sponsoring them inland?
If what you are saying is correct, and their job is not to seperate families, then how come they are so hesitant on giving TRVs to spouses of residents / citizens? If I were to say in the TRV application that I wish to sponsor them, it would have immediately been rejected. Thanks
CBSA and CIC do different jobs. One administers (CIC) and the other enforces (CBSA). CBSA officers do not make decisions on TRV applications. Since that decision has already been made by CIC they are not likely to overrule it (unless there are issues with criminality) but may limit it as I said before. Tell the truth when they ask these questions.
Look, I don't counsel people to lie. The choice is yours. But CIC didn't fall off the turnip truck. They knew when they issued the TRVs that there was a possibility of sponsorship in Canada when they issued them. They were just satisfied that your wife and child would abide by the laws and not overstay. Applying for sponsorship and applying to extend status is not overstaying. It's allowed. Probably unbeknownst to you, the VO likely took a look at the genuiness of your relationship by information given, i.e. length of marriage, length of time living together, the child, etc. For many couples who apply for a TRV for their spouse, the bona fides of the relationship have not yet been established nor whether or not the couple is self-supporting. More goes on under the surface than you know.
I know it doesn't all make sense. Immigration is a crazy world. But you've gotten past one hurdle. Don't screw it up by being dishonest with CBSA. You risk misrepresentation and having an exclusion order issued for your spouse and then that's a world of hurt for you.