I'm not totally sure about Securekey, as I used GCKey but I'm pretty sure you HAVE to log in to something in order to pay. Either way, you have to log in to either a GCKey or Securekey to link the application. Again, I didn't use a Securekey but I'm pretty sure you only need a Canadian bank account to use that. Once you have that figured out, you click on 'link an application'. I used family name, given name and DOB. (Make sure you are using the principle applicant's info, NOT the sponsor)
As the principle applicant, I used my last name as the family name and first and middle name(as that is what I put on my application) as the given name. For the birth city, I simply hit the spacebar once so I wouldn't have to type anything and then just selected the country (USA). Filled in the info for where I plan on living in Canada (again, using the info I provided on the application). For number of applicants I put "1". Many people have trouble with that part and find putting "2" even though it SHOULD be "1", has helped them.
I hope this helps!
