IndeedMind, you CAN build trade canals in EU3. They're called "Canal" and they're a province improvement .
Canals allowing movement of large fleets are a different thing.
Buy and install DW today and you will be able to build a a super giant swimming pool in Panama! It gives 10% bonus to the province's trade good value and is also prerequisite to Road Network, Post Office and Customs House! Because swimming pools are cool like that.