My oldest son, 15, wants to life with me and I live in Canada, can I get custody?

You may apply to the court for an order permitting your oldest son to move from IL to Canada despite your divorce 11 years ago. You are correct in your assessment that you will need an IL attorney.  As for being able to get the court to enter the order that you seek, the court is going to do what is ultimately in the child's best interest, not your interests, or your ex's interests.  There will likely have to be a hearing.  the court will also appoint a guardian attorney to represent your son.  the court will hold a hearing to determine whether uprooting your son and moving him in with you will be in his best interests.  Given his age,  and your ability to provide better for him there may be a chance.  however, if there is going to be a language issue in Canada or some other conflict as for his schooling, the court may not permit the move.  You must show that your son's life will be better in Canada and he will not be very affected by the move.