I am holding a reservation as follows:

KHI PK DXB BA LHR BA YYZ AC YUL AC YYZ BA LHR BA DXB PK KHI

However, my TA said he can't ticket because

i) AC flights cannot be issued on PK stock
ii) PK flights cannot be issued on BA stock
iii) ticket cannot be issued on AC stock

My question is:

can I re-route


KHI PK DXB GF BAH BA LHR BA YYZ AC YUL AC YYZ BA LHR BA DXB PK KHI

and have the ticket issued by GF? Simply put: how do you know if a ticket can be issued on xxx carriers stock. Does it have to be first international carrier? First over water? Any carrier?

Thanks!