So yeah, the PayPal DCC opt-out is still possible from the payment page. However, you can apparently only do so from a PC and not from a mobile device; there's no hyperlink to do so on the latter. (At least for eBay purchases, anyway.)

Desktop PC screenshot:




Android app screenshot:



EDIT: while I was messing around with getting the screenshots, I also noticed that the change in currency choice didn't actually save. Maybe it only does so if I go through with the purchase?

BTW, I now have a pending charge of $14.77 on that C$19.59 according to Chase. eBay/PayPal's currency conversion was offering $1 to C$1.2768 (or $15.34) had I opted for it.