As stated in the immigration site you need to pay the visa fee along. Whether you are submitting the form by mail or in person visa fee has to be submitted along in addition to CVAC service charge.
When you submit your documents to the Embassy get your passport, photographs, and all required documents. Most importantly get the suitable mode of payment which is accepted in the Embassy. The documents which are to be submitted should be attested by a notary public.
Once you are at CVAC you need to pay the service charge and hand over the complete application a receipt will be given back to you which will have your tracking number. This number is important to check the progress of your file.
After this whole process, a notification will be sent asking you to submit your passport. You will have to give the passport along with a passport request letter. Make sure your passport has empty pages for stamp and passport is in a good condition.
Passport can be sent through an authorized person at the CVA or one can go direct and hand it over to them. With the passport, a passport request letter, courier fee or passport transmission fee has to be submitted along. Even VAC consent form and personal details like email id, the phone number is to be mentioned along.
While you have to take you passport, either go or take it yourself or through an authorized agent at CVAC. The passport can even be returned to the courier service at the address you have mentioned.
For children, one need to attaché letter of sponsorship by parents and their respective passport details. Children are dependent on parents so a letter by parents is a must to get the visa.
This is the entire process to get through Canada Visa. To ensure that you get a Canada Visa at the first attempt, make sure you have all the required documents handily available. Once you get the visa, enjoy your trip in the Maple Leaf country.