to the best of my understanding, if you seek a TRV, you need to apply in advance of your trip... if you do not have the proper access permissions (visa) affixed in your passport, i don't think they'll even let you on the plane, will they?
i could be wrong, but i think you'd better look into this prior to buying a ticket and making the plans... the biggest obsticle you will come to is getting the visa, not passing immigration into canada... i've not heard of anyone who has gotten a TRV then been denied access (i'm sure it does happen, but not as often as those who come from visa-exempt countries and say something inappropriate at the border (i.e. they are going to visit fiances while they have all their personal belongings packed in their truck)... i think once you get the TRV (esp a single entry, vacation one), you've already satisfied the right people that your purpose is a legit one and that you'll leave...