Just to clarify, Foredeck is perfectly correct that you should go by the Notice of Assessment. But think of it this way: The Assessment is conformation that the tax return "looks" to be in order. The tax return itself has a lot of information that you may need to look at, particulary if the person is self-employed or is claiming considerable work expenses.
A tax return might not withstand a full audit, even if it received approval with a Notice of Assessment. Let's face it, even with the best, honest, intentions, we all can all screw up our expense receipts, deductions, etc. So the Assessment itself, even CRA would challenge it and audit if next year something shows up to raise a flag.
For Family Law purposes, you can challenge anything even if the CRA accepts it, or you can accept it if the CRA challenges it. You might consider the cost of a challenge, vs the amount of possible change in a support order. Is it worth it?
So for me, I would look at the tax return primarily, but demand a notice of assessment to verify that the return is acceptable, and then take it all with a grain of salt anyway. You know what your spouse does for a living, the type of expenses etc and you will want to raise your own red flags if you see something fishy.