Here in the UK Vagifem would be the equivalent of Imvexxy but Vagifem is only in a 10 mcg not a 4 mcg as well.
Personally I would use the Imvexxy at 10mcg that you have been offered as that is the localised oestrogen which may have the more direct effect on the tissues rather than systemic.
You probably do need a cream as well to rub on the area lower down that you notice burning. Use of Vagifem alone never reached my vulva area at what ever level I tried or for how long My problem is vulvar.
Have you got an estriol cream in Canada to try or only the Estragyn which is estrone ?
I use Aproderm a barrier cream when peeing on the vulva becomes a problem at times.
Have you reduced tea, coffee, spicy food ?