It is great to hear that you and your horse have much such great progress!
I know how you feel not having people around to work with - up until this Monday, I have been agisting on a property on my own, for a number of years.
It is SO helpful to have a pair of eyes on the ground, that know a bit about Dressage and how a horse should move - as a rider sometimes we get so used to something that our horse does, that we don't pick it up as a fault until someone else tells us.
As for what you could do now, I would start working him in the arena again under saddle. Doing LOTS of trot work with millions of transitions, changers of rein, and a stack of leg yield and shoulder fore work on straight lines and circles. The more of this type of work you do with him, the more he will be balanced and supple enough to carry a canter.
When you do go to ask for canter under saddle again, I would be standing off his back and staying on a nice wide 20m circle (or bigger if space permits) - avoid too many straight lines for now.
A great way to set a horse up to canter on the correct lead, in balance, is to leg yield them into the canter transition.
Trotting on a 20m circle, in a nice active, forward trot. Leg yield off our outside leg onto a 15-18m circle, then start to leg yield back out off your inside leg. When you get close to 20m, ask for canter, and only canter for 1/2 of a circle, before coming back to trot and repeating the exercise.
Don't overdo the canter work at this point, just sprinkle it in here and there for 10-20m at a time. You don't want to canter a long distance and have your horse fall onto the forehand, thus losing balance and encouraging him to disunite.