My team is exploring upsource as our review tool. But I can't find a way of adding commits from different projects in one review. Is is possible to do that in upsource? That is a really import feature for large projects.
Upsource is supporting large projects via multi-root specification. For example, Intellij Community project includes android repo and adt-tools-base, besides the main repo. So if your repositories are really part of one project, it's better to set them up as one project.
If you really need to have several projects, you can always create parallel reviews and cross-reference them.