That all depends where you make the reservations from.
For your Nice to Paris trip, make the reservation at www.tgv-europe.com and select either Canada or Great Britain as your country, and select that you will pick up your ticket at the station. You can then go to a ticket booth, show your credit card, and pick up the ticket before boarding the train. As a result you will pay the same as Europeans would for the ticket, no more.
For the Paris to Amsterdam route you can use www.thalys.com to book it.
As for the two Spanish trains, I do not know off-hand but I am sure someone else can respond to that shortly. At minimum, you can reserve your Spanish train trips from a train station in France, as you can book for major routes anywhere in Europe from any major train station.