Contact your regional agricultural officer. Since Ottawa banned nearly all effective chemical pesticides perhaps they could be kind enough to supply us with biological controls,(also not available here)
Parasitic wasps come to mind.
I'm sure they will have several alternatives and complete instructions for use if you call.
Remember,the government is your friend!

Bob

I have used Neem oil on several houseplants, indoors and out and it's generally well tolerated by plants and safer than chemical insecticides. The only downfall I find is that sometimes you must do multiple applications to totally get rid of the bugs (say aphids). But, as it's a natural oil, I don't mind and I would rather spray twice with it than, say, with a harsh chemical like cygon or malathion.

As I only have to spray a few houseplants, I mix neem in smaller quantities, in a spray bottle, a tablespoon of concentrate mixed with warm water and a small bit of dish detergent (helps disperse the oil in the water). Shake and then spray. You can sometimes find it pre-mixed as well, but the bottle of concentrate goes further, you just have to buy your own spray bottle.

Not sure if it will work for Leaf Miner but worth an experiment to try.

Leaf Miners are nasty business. In my area whole stands of birches are gone due to them. The miners get in between the layers of the leaf and do their terrible damage. The standard treatment used to be Cygon 2E which is a systemic insecticde applied as a soil drench or painting a band of the stuff as high up thr trunk as you can get. I'm not sure it's available to the public anymore. You used to be able to get it in small quantities. In larger quantities you had to have special licence. Spraying a 30' tree will be quite a challenge. As Bob says get in touch with you regional AG. office. Best of luck.