I'm looking for some answers on how to proceed, I'll give a…

Hello:
Sorry, I did not get the full message until now.
You should send a written letter or email to him, keeping a copy for yourself (best is to send it to every address you have for him so it can not realistically try to say he did not get it) in which you demand that he disclose to you within 30 days copies of his income tax returns as filed with CRA for the past 3 years, together with any Notice of Assessment and Reassessment received in those years, a copy of his year to date pay stub, and a copy of all other financial information from the past 3 years with respect to any other source of income, as required by the Federal Child Support Guidelines. That would include financial statements for any corporation or business that he controls.
I usually make it clear in such letters that if this is not provided, that an application to court will then be made to seek this information, and an order for child support, plus an order of court costs.
My expectation is that you will likely have to start a court proceeding to either get this information, or to get an order in place that he will pay. There are red flags here certainly that you are dealing with a difficult person who will probably make you do this the hard way rather than agreeing to meet his obligations under the law voluntarily. But sending this type of letter can at least help in getting an order of court costs, and to set a date from which the court may order retroactive support. The court may not decide to order retroactive support unless there is some indication and proof that you put him on notice that you expected the guideline amount to be paid.
You could also demand in such a letter that he turn over tax returns going back further than 3 years if you want. The normal disclosure under the Guidelines is 3 years, but a court can order him to disclose more if retroactive support is relevant.
You should certainly take steps to apply in court for retroactive support before your child is 18, as the law says that once a child is no longer entitled to child support (which is often at 18, although if she is disabled or attending school full time beyond age 18 she could still be entitled to support for a number of years) there is no way to claim retroactive support.