Is it my daughter’s right to have proof of address/hotel of where her Ex is taking their 3-year-old son every other weekend before pick up?

Generally speaking, No – at least not without an agreement or court order, clearly stating that your daughter has the right to specific level of detail.

Under Canadian law, each separated and divorced parent has a general right to know where their children are when the other parent is exercising parenting time.   However, this does not mean that the other parent must hand over an itinerary, or must scrupulously account for their time or activities, or invite consultation.   The prevailing philosophy is that the parent who exercises parenting time is entitled to make all the usual and necessary parenting decisions during that period, as is appropriate to attend to the child’s well-being.

That said, it is always good practice for both parents to cooperate with each other; for example by advising if the child is going to be left with babysitters or friends when the parent is not there.  The level of communication may also vary according to the age, needs and best interests of the child.