Here's some answers based on the US's National Electrical Code. You will have to check your Canadian Electrical Code to see if there are any differences.
You must have an EGC in your feeder to the shop; any connection through the earth only does not provide a sufficiently low impedance fault path to trip breakers at 120/240V. The NEC would also require a grounding electrode system at the outbuilding supplied, which is connected only to the EGC; there would be no neutral-ground bond on at the outbuilding, just the single such bond at the electrical service.
If you are using a short length of PVC conduit as a sleeve for a cable wiring method, with the cable entering one open end and exiting another, then the only limit is what you can make fit inside. Depending on the length, you could try using a cable diameter up to 75% of the inner diameter of the conduit. Which is 1.03" for Schedule 40 and 0.94" for Schedule 80.
For THWN-2 conductors, the cross-sectional areas of insulated conductors in mm^2 are #10 = 13.61 ; #8 = 23.61 ; #6 = 32.71 ; #4 = 53.16. For conduit with 3 or more wires, the allowable fill is 40%. That works out to an allowable fill in 1" Schedule 80 PVC of 178 mm^2; and in 1" Schedule 40 PVC of 214 mm^2. So even in Schedule 80 PVC, you could fit (2) #4 copper for the ungrounded conductors; a #6 grounded conductor (neutral); and a #8 EGC. With 75C rated terminals that would suffice for an 85A feeder, which may be protected with a 90A breaker (or, oddly, a 100A breaker if on a 100A residential service), so long as the maximum unbalanced 120V load is 65A or less. E.g. if the total load is 65A or less, or if you have say 20A of 240V 2-wire loads.
Aluminum conductors are more cost effective, and filling the conduit less will make the pull easier. Maximum 360 degrees of conduit bends between pull points.
Cheers, Wayne