FYI- When traveling to Mexico you are NOT allowed (by customs) to bring three camera bodies unless you are traveling with another person. Even then I only bring two since that's all will fit in most hotel safes. Also limit the gear you bring in to less than $10,000 total (this includes bodies, lenses, flash, batteries, CF cards, your laptop, etc.). This isn't exactly a rule but if you get pulled aside by customs it makes it less questionable. I always bring my back-up gear with me to Mexico- my 5Dc and my 7D (used to be my 40D but I sold that). Never the 5DII. And never a 70-200mm. Nothing says "I'm a pro! Rob me or arrest me!" like a giant white lens. Also don't forget your receipts or proof of ownership of these items in case you're given issues coming back. This has never happened to me, but I've heard it happen to others so I always like to be safe and bring it.
When going to Mexico you need to find out a few things before going down:
1) Does the resort allow outside vendors? If they do, how much do they charge? Technically the bride and groom should find this out first, but I recommend taking a look yourself to see what the rules are. You can still shoot somewhere that doesn't allow outside vendors. Just make sure you get introduced as a friend, not a photographer! If the wedding is outside of a resort you have less to worry about. But resort contracted photographers usually aren't too happy when a non-Mexican flies in for a day and steals their work. And you can be arrested for it.
2) I'm not sure what the Canadian rules are for working in Mexico, but I recommend finding that out. You may need to get a temporary working Visa (which you can usually get at the airport and isn't too expensive) which allows you to safely work in the country without getting arrested.
I've shot 4 weddings in Mexico in 2010 alone and never had any problems. But I always advised the bride and groom to introduce me as a friend when resort employees may be able to overhear. Even if I'm there legally I don't want to step on anyone's toes and I found when I was introduced as a college friend of the bride who also likes photography, and not as a pro photographer, people cared about me less.