I suggest Brazilian Jui Jitsu, pop the cap in someones elbow and when the others hear the guy screaming like a women they will go and f**k off like they should do. Start taking Muy Thai for a standing fight and rely on the BJJ for ground. These arts are no nonsense and very effective on the street, they are not the "kick people off a horse style" like Tai Kwan Do, REAL karate is good, not american, Shodukon is real stuff. I would suggest to the several people in the group that you take them on one at a time and question whether they are real men or not, it takes a loser with penis envy to fight 6 on 1. Make an example of the biggest one if you have to. I am 6'3" 280, and my bro is 5'10" 160 (hes all muscle) and we use very similar styles and are deadly effective, so size can be varied for these arts too. You do not have to be a massive person. The quickest fight I got in, was very similar to the people you are describing, they bugged me I kicked one in the stomach so hard that he barfed and got knocked into a wall and had a concussion, they did not bother me ever again, and when they tried messing with other people I would step in and they quickly changed their habbits. I grew up having to use the martial arts I know and I know that they are effective on the street and in a no rules fight.
Wing Tsung is good but takes years to be effective, I would suggest the red boat style, Frank Gucci, a Seal trainer uses it and trained with my teachers, Wing Tsung is the ultimate in a bar fight, it is what Bruce Lee's style of punching comes from solid, fast, and very effective. There are many lists of martial arts schools that include canada online, all you have to do is search, and I would suggest you get an ASP Defender key chain if you want pepper spray, its very small and concealable, www.selfdefenseproducts.com