I would like to know if there is some legal stuff I should fix with Canonical in order to make my distro publicly available as it is based in Ubuntu. Thanks.
You have the right to modify and redistribute Ubuntu under the GPL.
As long as you don't infringe any trademarks like 'ubuntu' or 'buntu' for example calling it 'Jorge ubuntu' without permission, or claim to be officially endorsed or assiosiated with Ubuntu / Canonical then you should be fine.
You should read this link for clarification and contact Canonical if you are unsure.