If there are no local restrictions, it should be fine to fish non-metallic cable to feed a sub-panel.

Would fishing of #4/3 non-metallic cable to supply a sub-panel be allowed in Ontario Canada?

If it is allowed, is this the way an experienced electrician would do it?

What would be the largest breaker size I could use on the main panel to supply the sub-panel via the #4/3 non-metallic cable?

Thanks

In Canada you can fish cable to a subpanel. Using #4 will only allow an 85A max current. Since there are no 85A breakers, at least none that I've ever seen, I suggest you use #3 cable, which will allow a 100A DP breaker to feed your sub.
3/3 cable is thick and very heavy. Good luck fishing that.

"3/3 cable is thick and very heavy. Good luck fishing that."

Are you suggesting it's not a practical solution? Would it be worth trying?

The way I see it there are 3 options:

(1) Fish the cable if feasible, as discussed above.

(2) break the finished ceiling, install the cable properly, and fix the ceiling.

(3) Another option is to run the wire on the outside of the house. It can go straight out the wall where the panel is and then run along the side of the house at ground level about 20' towards the back of the house and then through the wall and into the part of the basement where the sub-panel would go.

If option (3) is a good way to go what type of wire and conduit should be used? Can it be run at ground level?, installation details?

Any comments/suggestions would be appreciated.

I'd like to know how a good experienced electrician would do this, i.e. go for option (1), (2) or (3)(or another option?) and how would you go about it.

Thanks again.

3/3 is what you will need. If you dont mind putting in a small bulkhead, I'd consider that route first. If not come off the side of your existing panel with 1-1/4" conduit use LB's instead of elbows and remember to unbond the sub panel.

2/3 USEI90 is cheaper than the 3/3 copper. If you can dig a trench easily I'd go that way.

If I run the wiring outside:

Can I run it at ground level?

What kind of conduit would I need to use - steel or plastic or either?

What type of wire would be best to use?

Any other comments/suggestions would be appreciated.

Thanks

I'd go slightly above ground level, check your local code, steel or PVC is OK, THWN wire in the pipe.

O.K. To summarize:

*I want to install a 100 A sub-panel supplied from a 200A main panel.

* The sub-panel location is about 40'from the main panel. I'd go straight out the wall where the main panel is and then run along the side of the house at about ground level about 20' towards the back of the house and then through the wall into the basement, and another 20' to the sub-panel.

* What wire (type and size) and conduit (type and size) should I use?

Thanks