Well in Canadian spousal sponsership,financial establishment is not required (according to the website).
It's very strange that they have pointed your apllication on financial grounds.Is your hubby sponsor or principle applicant .
Regarding the marriage proofs ,I recon you should start gathering quality proofs ,old phone call records ,emails ,boarding passes ,photographs ,marriage album,hotel bookings ,receipts of gifts exchanged.If you are called for an interview just provide loads of proofs to NDVO,because according to the previous interview candidate's experience they basically looking for quality and quantity (proofs) in interview .Be rest assured ,you have a true marriage ,then no one on this planet can deny your reunion with your life partner.
Waheguru will bless you!!!