I am a Canadian citizen and have family living in Montreal, but personally have been living abroad in Kuwait for 20 years, I am planning on moving back but am not sure how to transfer my son (who was born in Canada and is a Canadian citizen entering his 12th Senior year) to a high-school here. He attended a Arabic/English bilingual school in Kuwait. Any information would be appreciated.
What curriculum was your son studying in Kuwait? Was he at an international school? If at all possible, it's best to stick with the same curriculum, especially so late in your son's school career. International schools offer foreign curricula so they'd be your best chance at this. For a list of schools, see our International Schools in Montreal page. Even if there isn't a school offering your son's curriculum, international schools will at least teach in English. Fees can be high though, so if this isn't something you can fit into your budget, English-speaking subsidised private schools are another option worth looking into.
Public schools in Montreal usually teach in French, so I wouldn't recommend that route in a case like yours. There are some public schools that teach in English rather than French but there are strict rules about who can attend these. Although since you're an Canadian citizen, your son may be eligible to attend a public bilingual school. Someone else asked a similar question on this forum a while back – you can read my answer here. It includes some links that may be useful.
Best of luck.