If you wish to extend your stay you should submit a request for an extension of status at least 30 days before the expiration of your first stay. This can be done online and is $75.
Excellent replies by Pinklady and AmericaninQuebec.
I applied outland - and, as you can see from my data, it took ~9 - 10 months to process.
One thing - if your husband is not issued a Visitor record; i.e., he enters Canada without a stamp in his pasport and thus has a 6-month visit period "by default", the above is 100% accurate.
However, if he is issued a Visitor's Record (VR) by an immigration officer when he crosses (a possibility - and a
good thing in my opinion) then he may be able to extend his Visitor's Record by visiting the
Canadian side of the border (
without crossing to the U.S.) for
free. He should do so about a week before his VR expires - ask the immigration officer when/if he is issued a VR to be sure - they can renew it in about 15 - 30 minutes. Be aware that they will want to see progress toward your PR, or they may not extend the VR.
Personally, I was assured by the Immigration Officer that first assisted me that they would extend the VR without an issue, so long as progress toward PR was evident. I extended mine twice during my PR application period for 6 months without any problem whatsoever and was thus able to visit my wife whenever I wanted without problems at the border. Be sure your husband carries copies of all of the documentation pertaining to your case with him whenever he crosses the border, and when he requests an extension of his VR at the Canadian side of the border.
Personally, I found that the Immigration officers I interacted with were extremely understanding and helpful. It was really a good experience.
Be sure he knows how to get to the Canadian side of the border without crossing into the U.S. - I know how to do this for the I-89 (Vermont / Highgate) crossing - others might be able to help if he comes across the border at another location.
Feel free to PM me if you have further questions.
Take care,