You can add the ST3/Python3 branch (where available) to Package Control via the
Add Repository command and then install. Repositories take precedence over packages in Package Control's library.
For example, to install the ST3 version of FuzzyFileNav add the following branch: github.com/facelessuser/FuzzyFileNav/tree/ST3
And then install via the
Install Package command.
Notes: not all packages have working ports or at all. Remove the ST2 package first, if you've installed it by mistake.
Hope this helps,