If I fly from Toronto to Hong Kong then to Mainland China for 144 hr

In order to be eligible for 144 hour visa free transit in Guangdong province, Zhaoqing included, you will have to fly from Hong Kong to Guangdong and then travel to Zhaoqing overland. Simply speaking the only way to be eligible for this visa free transit scheme in Guangdong province is to fly into one of three designated airports within the province. Also, you should be aware that you cannot exit from Guangdong province to Hong Kong because that would be a return trip and not a transit. In another words, you will have to exit to Macau by ferry from, for example, Shekou port in Shenzhen. Also, to be eligible you would have to buy your ferry ticket in advance, even before you have departed from Hong Kong toward mainland China. When you reach Macau, you can return to Hong Kong.

These same rules are valid for your second visit to Zhaoqing as well. By the way, it is fine to use 144 hour visa free transit scheme in a row because there is no limit on how many times you can use this scheme within a certain period of time.

You are allowed to stay with your friends. Upon your landing in Guangzhou, you will present to the immigration the address where will you stay along with the full name and the phone number of your friends because the border authorities may decide to make an ad hoc check. Also, you will have to register yourself within 24 hours after your arrival within the nearest PSB (Public Security Bureau) and the best way to do that is to come there accompanied with your friend because of the language and the procedures you are not familiar with.