I think the easy way is to create a virtualenv for you project and rely on it after
/usr/bin/python3 -m virtualenv
--system-site-packages -p /usr/bin/python3 /cloud/project/myproject
In your virtualenv, you'll have pip3 available with python3.
You can continue to use the terminal or use reticulate
use_virtualenv('myproject', required = TRUE)
or any of
https://rstudio.github.io/reticulate/articles/versions.html
Nota: virtualenv_create() does not work as expected. I did not have time to open an issue yet, but terminal is better here.