I live in the US so my help is dubious.
Wendy, I would suggest talking to a lawyer experienced in custody issues. First, do you have custody and he has visitation? Or, do you have joint custody? Theoretically, the court system would hope that you and your ex could work out your own arrangement on religious training. If not, then the court would have to decide and that can be a long, difficult, and expensive road. I would suggest considering the following:
1. Is she old enough under Canadian law to make her own religious decisions? (If she can decide to be baptized at 10 according to JWs then she should be able to decide not to go out in field service IMO--which of course is not law just my opinion. Of course, then he would have to make arrangements for her to be looked after while he engages in field service.) All this many entail going back to court and I am sure your ex will fight it strongly.
2. She has to make it clear to her father that this is her decision putting it in her own words (no prompting from you). He can still make her go...but he can't make her talk. He can insist she go to meetings, but it is her choice to participate.
You and she have to decide how much energy to put into this. I don't know how much time he spends with her...if it's every other weekend...she might be able to endure it.
The Education Brochure says (and it applies both ways)
*** ed 25 Moral Values That Merit Respect ***
Children’s Right to Freedom of Conscience
You should also know that Jehovah’s Witnesses attach much importance to the individual Christian conscience. (Romans, chapter 14) The Convention on the Rights of the Child, adopted by the General Assembly of the United Nations in 1989, recognized a child’s right to “freedom of thought, conscience and religion” and the right “to express his or her opinion freely and to have that opinion taken into account in any matter or procedure affecting the child.”