Failed because the floats were in such terrible condition. From the TCCA M&M Report:
Review of the aircraft’s technical record revealed that reference to required data relating to numerous observed repairs was missing.
There were numerous repairs to all the Deck Combings.
You aren't supposed to do repairs to the deck combings. It corrupts their strength.
There were numerous structural patches and evidence of sealant being applied inside the right float
Inspection of the float access panels indicated that there was no sealant in place
The float bottoms had a thin coating of paint over corroded areas.
Over a year before the crash the ops manager was arranging to have the floats completely overhauled and reskinned. The owner decided they couldn't afford to do it. But they flew another at least 1000 hours before this crash.