TRV doesn't guarantee entry because it is granted by an embassy, but the border is manned by Canadian border guards (different organization). This is normal -- there is no visa from any country in the world that guarantees entry, because the border guards always have discretion. Are people with student visas rejected for no reason at all? Unlikely, because the border guard can probably find a reason, if they want to. Will some of them reject you for no reason at all and then search until they find a small justification? Don't know. Can they reject you without their superior signing off on it? Don't know. Will the superior support them unconditionally? I'd bet on it in the States, don't know about Canada. Personally, I find it hard to believe that if you fulfill the conditions for entry -- visa, real course of study, proof of funds, etc. -- that you will get turned back. Remember that something like an undisclosed DUI is not getting rejected for no reason, it's that they find a legitimate detail that makes you inadmissible.
Just having the visa, though, does not make you admissible, it gives you one puzzle piece.