I am new to Python to bear with me.
Switch the role of 2 and 3 in this answer as appropriate.
Say you already have jupyter setup with a python 2 kernel and an anaconda environment with python 3. Activate the python 3 enviroment and then run
conda install ipykernel
After that you can select both a 2 and 3 kernel when creating a new notebook, or in a running notebook from the kernels menu.