since I dont have US Visa , i will apply for PRTD with H&C and in case of rejection , will reapply from scratch.You only have 2 options.
1) apply for the PRTD and take your chances, with or without H&C consideration.
2) cross the land border from the USA via private transport. Obviously, you will need a US visa.
Regardless, your third child will need a separate visa for Canada.
thank you all