No - there is no minimum. Whether you are allowed into Canada and for how long is entirely in the hands of the CBSA official you speak to at the border. If you are planning on making long visits to Canada, you should be able to demonstrate that you have sufficient funds to fund your stay and also show that you have ties back to the US (e.g. property owned, etc.). Keep in mind that you are only allowed to visit Canada. If the CBSA official suspect you may be trying to live in Canada without authorization, you could run into issues entering the country. Also, make sure you purchase travel insurance to cover yourself for emergencies. Medical care is extremely expensive in Canada for those without health care coverage.
