Were you cited for underage consumption of alcohol? If not, then it is not necessarily a bad thing. It is something that will be questioned on your background, but lots of people drink underage. (Which is not to say I condone it)
As Cufnstuff said, check your credit. Too much bounce there. My three scores are within 30 points from high to low. 150 points is too extreme.
Admit the weapons violation in your interview / background. As no action was taken by the Mexican government, (and your buddy bribed his way out of it so there is likely no record to be found) it should not be an issue. Honesty requires you mention it. I do not know anything about alcohol and Canada, so not comment.
Your orientation is irrelevant and need not be mentioned. This is not the US military. It is neither pro nor con here.
Poly and CVSA are simply to see how honest you are during the process. Everything that will be on the poly (I have never seen a CVSA, so no info) will be asked prior to the exam itself so you can explain anything that needs to be. They are not out to surprise or fail you. They will ask the same question (about 15 different ones total) in various ways. Be honest and don't think they are simply out to get you or they think you are lying.
Good luck.
You're allowed to have a life, you know. I read it in a manual somewhere. - Eugene Matuzak - Timecop