As a CP on US, how hard is it to upgrade to Envoy to Europe? Is the chance of upgrading more or less 100%? Would a CP companion upgrade probably clear in advance as well?

The last time I went to Europe was 2 years ago and I took UA and E+ rather than running the risk of being stuck in E- on US.

If I can't upgrade on US, I might as well go for one of these CO fares.

Thanks.