Ummm, let's start with some theory so you can understand ^^
In Canada there's few mobile companies, and the main ones are Rogers and Fido. Fido is owned by Rogers, so you could say we are talking about the same company here, but I've read a lot that service in Fido it's terrible! so you should stay with Rogers if you can.
Both Rogers and Fido are GSM companies, so you should be able to use you GSM phone there (the one with a SIM card), BUT you should be careful with the kind of phone you are using, because these companies work in frequency bands. There are 4 frequency bands, 850, 900, 1800 and 1900.
If you have a Quad band phone, your phone supports all 4 bands, so you can use it with any company and if it's unlocked, you can even use a SIM card from any GSM company. Now, if you have a triband phone you are in a little bit more complicated situation, because your phone can only support 850/1800/1900 or 900/1800/1900. Let's think for a moment that you have a 900/1800/1900 and you are going to a country where the only GSM operator works with the 850 frecuency band, in that case you wouldn't be able to use your phone :(
Now to the main problem with Rogers... Rogers used to work with the 1900 frecuency band, so you could use almost any phone there, but tomorrow (October 1) it will officially change to the 850 frecuency band! So if you were planning on using your triband phone there, better to check the frecuency bands your phones work ;)
If you are in Venezuela, I'll give you a little hint, Digitel works in the 900 frecuency band and Movistar in the 850. I have a Digitel triband phone, so I have a problem ^^ I have to sell my mobile phone and buy a new one there, since this one won't work in Toronto :)
Did you checked yours?