I do not know the rules in Canada. And it would be helpful if the FULL rule book was read and not just one line. That being said:
Banamine is under scrutiny in the US due to its abuse and misuse. Withdrawl time, regardless of country, has not been established if the drug is given IM, or Sub Q. Only IV use is approved with a withdrawl time.
Banamine definitely gives an animal an advantage, that is the purpose of the drug.
Even if a vet prescribe the product, it is no excuse, as the exhibitor is responsible for knowing the rules and following them.
Listing the forbidden drugs would be fruitless. Because there would always be a drug someone would find or come up with and use it, then use the excuse "but it is not on the list". Heck, it would be human drugs, PED's, equine drugs, etc. Maybe they should do the opposite, and list the drug(s) that ARE allowed, which would be a very short list indeed, especially if it is a terminal show.
The excuse of "everyone is doing it" about makes me ill. The problem with this country is there are too many FOLLOWERS and not enough LEADERS. I would like to think that people would not do something just because someone told them to: Would you hit a baby because someone told you to? Would you jump in front of a semi if someone told you to? Would you steal someone's show equipment if someone told you to?
Please be your own person and do whatever you want to do because YOU feel it is best for you. And then make sure you take full credit, regardless of it is good or bad.
Also, please keep in mind that cheaters generally hang around other cheaters. I have recently heard of two families that have totally went of the deep in (IMO) and now people are avoiding them because they do not want to be associated with them. One family has a very successful business in the cattle industry and it is in serious jeopardy. Honest people do not want to be caught hanging around and being friends with liars, cheaters, and rule breakers. Remember, its YOUR decision, YOUR life, and YOU will be the one that has to deal with the consequences. Make sure you're willing to pay the price.