hmm is the canister located above or below your aquarium? i expect that once the canister is full and you point the exhaust tube to the tank, turn it on and it should start flowing? or did you mean that the exhaust flow is only a trickle? are the valves of both intake and exhaust fully open?

if the flow is still weak you may have to check the impeller motor and clean it... Make sure the cap is aligned properly with the canister when you close it again.
/crosses-fingers
PS. looking again at the pictures i noticed that you may have your media installed in reverse. the mechanical filter (foam/sponge) should be at the bottom, then the chemical in the middle (
activated carbon), then the biological media at the top (bio ceramics).