For a PayPal account, I'd go with Premier unless your business is really, so popular and you get like 5+ orders everyday, then I'd go with the Business account.
Umm, since you accept payments through PayPal, it doesn't really matter unless your paying for your shipping via Canada Post, which is basicly the only PayPal integrated shipping carrier for such things like eBay purchases.
3 Carriers: I'd say: UPS, FedEx, and DHL.
And it wouldn't be a good idea to use shipping carriers integrated with PayPal (simply because Canada Post is the only one I know that is) and you'd probably end up going to your post office or local UPS store or FedEx or requesting one of the carriers to pick it up at your house and pay there rather than pay via PayPal as I don't know any shipping carrier that you can pay via PayPal easily instead of pulling some string. You know.
My experience with UPS is much more better than FedEx. I just shipped 2 packages from WA to IL, the same driver took them at the same time, but one delivered on time, and another one 2 or 3 days later without any explain. One of my hardware vendors is using FedEx too, and once late shipment (on FedEx side, my vendor sent on time)