Jupyter Notebook is loading incorrect Python kernel

I am on OSX Sierra (10.12.5), and am using Jupyter Notebook v 4.3.0. I have installed both Python2 and Python3 using Homebrew, and both kernels for Jupyter Notebook. Upon opening the notebook to use Python3 kernel, I find that it still uses Python2.

I might be missing something obvious in my installation, but I can't seem to figure out what it is.

## Detailed Description

### Installation:
I installed both Python2 and Python3 using Homebrew, and Jupyter Notebook on my system thus:
`brew install python3`
`pip3 install --upgrade pip3 setuptools wheel`
`pip3 install jupyter`

I ran all analogous commands for Python2 as well.

### Configuration:
I generated the config file using
`jupyter notebook --generate-config`, and the only configurations I have "enabled" in my config file are:
`c.NotebookApp.browser = u'safari'`
`c.NotebookApp.password = 'sha1:somepwd'`

### Both kernels installed:

Both kernels seem to be visible to kernelspec:
```
jupyter kernelspec list
Available kernels:
python2 /usr/local/share/jupyter/kernels/python2
python3 /usr/local/share/jupyter/kernels/python3
```
Both kernels are also available as options when I start execute `jupyter notebook`:

As an additional check, `pip list` and `pip3 list` both include `ipykernel`.

### Problem:

When I opened a new notebook using **Python3** kernel, none of the packages I installed using `pip3` were recognized when I used `import`. Furthermore, `sys.path` returns path to Python2:

When I run `print "Hello World"`, it gives me a successful output (which is true in Python2, but should throw an error in Python3).

*However*, when I use the (depreciated) command `ipython3 notebook`, things work as expected:

and all my Python3 packages are successfully recognized.

It doesn't seem to be the biggest deal breaker, as I can continue working with `ipython3 notebook`, but I wonder what I am missing that causes `jupyter notebook` to not load Python3.

Reproduce the behavior using the listed Homebrew, pip, and pip3 commands, then compare `jupyter kernelspec list`, a notebook started with `jupyter notebook`, and one started with `ipython3 notebook`. Check whether selecting Python3 actually uses the Python3 kernel and can import packages installed with pip3; the issue is resolved when the selected kernel reports Python3 paths and behavior.

Written by the indexing model from the issue text.