In Brisbane only Norfolk Point (the north side of the entrance to Manly Harbour is not effected by tides (except in a extreme low tide) as you access the water down steps from the breakwater. Everywhere else is badly effected by low tide.

I'm not sure about the Gold Coast and Sunshine Coast. The surf besches should be Ok and most of the Broadwater if you look out for sand banks.

Refer the URL below which provides good information on locations around Brisbane

boardcrazy.com.au

Apex Park or Pelican Park Woody Point maybe. I have seen the odd SUP rider out there on a low. not sure of the depth though.