Actually the US laws concerning 3D rendered CP is it's legal as long as you don't present it as being real. If you distribute it as "3D rendered CGI lolis taking it in the pooper and chewer" it's legal. If you create photo realistic render and try to distribute them as actual CP then it's illegal.
There was a case I saw on a TV news program a few years ago where these internet vigilantes made this pre-teen girl in Blender that they controlled through a video chat program and it could perform various animated sequences if requested like undressing, lifting up the shirt, masturbating, showing butt, typing, etc. They added a lot of video noise and bad compression like you'd get from a cheap webcam to try and cover the fact it was Blender using Daz models. They would then video chat with these pedos and record the pedos making requests for the 3D girl which they would then perform. They then took all the chat logs and turned them over to the FBI.
They ended up getting in shit for interfering with several ongoing investigations and the FBI told them that they were actually guilty of producing CP because they presented their chat animations as if they were real which is against the law and all the defendants would have to do to defend would be to say they could clearly tell that it was just a 3D rendered computer animation and not a real child.
In short, the feds don't have time for your vigilante bullshit.
As for Canada. The first case of a guy being busted for loli he wasn't actually busted for the loli itself. He was a sex offender and part of his probation was he was forbidden to buy, sell, or possess pornography of any kind. He ordered a bunch of Loli hentai from Japan and ended up back in prison for a parole violation.
There have been a few other people in Canada charged in round about ways for hentai related crime. There was a security guard in Nova Scotia who was working on a Canadian Forces base and he used his computer to watch hentai vids at work