Hi all, I'd like to provide some updates I got regarding my previous question.
1. I emailed the Canadian Consulate in HK to ask about this. I received two replies (1 minute apart). The first one said it's ok to use the photos taken in HK for my renewal applications sent from the U.S.. In the 2nd reply, it stated that "if you have your photos taken in Hong Kong, and plan to submit your application to another passport office other than Hong Kong, then it is up to the processing officer to whether or not consider the photos acceptable. Questions may be raised whether or not the applicant is within the jurisdiction of the passport office it the photos are taken at another country."
2. Then I wrote to the Canadian Consulate in the U.S., they provided me a list of passport photographers in those states that fall under the consular jurisdiction of the State I live in. However, they asked me to confirm with Passport Program if the photos taken in Hong Kong are acceptable in my case.
3. I talked to an agent at Passport Program. They confirmed that photos taken outside U.S. are ok as long as the photos are taken according to the specifications required (and I mentioned that the photography studio in Hong Kong is accepted by Canadian Consulate HK).
On the list of photographers, I found ONE Walgreens. I called Walgreens at that particular location. They confirmed that they had their equipment set up to take Canadian passport photos, and they will put the studio name, address and date. I guess this will be my go-to in order to avoid any unexpected rejection from Passport Program.