Can I travel between USA and Canada using AVR (each trip duration less than 30 days) multiple times while my visa appointment is scheduled?

Technically, you appear to meet the requirements of automatic visa revalidation as you have a current status, an expired US visa, and will be in Canada for less than 30 days on each trip. You may be questioned on the purpose of your frequent trips if there is some thought that you may be doing something illegal, but I do not otherwise see a problem. The fact that you have a visa appointment at the consulate scheduled for October should not affect trips done before the interview. Insofar as Canadian entries are concerned, I possess no knowledge of Canadian immigration law and cannot inform you as to whether there are restrictions. Due to the limitations of the Lawyers.com Forums, Alan Lee & Arthur Lee, Esqs.’ (the "Firm") participation in responding to questions posted herein does not constitute legal advice, nor legal representation of the person or entity posting a question. No Attorney/Client relationship is or shall be construed to be created hereby. The information provided herein by the Firm is general, and requires that the poster obtain specific legal advice from an attorney. The poster shall not rely upon the information provided herein as legal advice nor as the basis for making any decisions of legal consequence.