Being on the border of a gardening zone (cannas are considered winter hardy/safe from lifting in zones 7 to 10), it’s impossible to know absolutely whether your plan to mulch will keep them safe. (Think about this: heavy rain, followed by heavy freeze: you could lose the plants if the ground freezes or the rhizomes could become saturated and rot.) We would be inclined to lift the rhizomes to be on the safe side. However, because gardening is somewhat experimental, you could mulch as planned and see what happens … and, yes, lift the mulch after your last spring frost.
Being on the border of a gardening zone (cannas are considered winter hardy/safe from lifting in zones 7 to 10), it’s impossible to know absolutely whether your plan to mulch will keep them safe. (Think about this: heavy rain, followed by heavy freeze: you could lose the plants if the ground freezes or the rhizomes could become saturated and rot.) We would be inclined to lift the rhizomes to be on the safe side. However, because gardening is somewhat experimental, you could mulch as planned and see what happens … and, yes, lift the mulch after your last spring frost.