The FAA regs are straight forward.
You need 20/20 vision in each eye.
Glasses and contact lenses are allowed, with one exception Varifocal contact lenses or wearing one contact lens with an asymetric correction for reading are prohibited.
They dont care how thick your lenses are or how much astigmatism you have.
If you get an FAA First Class medical then you can convert it to a CAA medical if you meet the renewal standards for a CAA medical.
Incidentally there is no such thing as an initial FAA medical, each medical exam is to the same standards.
Waivers are easy to come by for most static defects, ie Monocularity, Colour vision etc.