You could still have a canal connecting two waterways, you'll just need appropriate technology (locks to regulate the flow of water) or an equivalent magical solution.

I can see two places for this on the latest map:

* On the northern part of the continent where two rivers flow to opposite directions (east-west) from the mountain chain. You'd likely need a tunnel to connect them though.
* To the south from the forest on the east coast. One river flows there to the big central lakes, another one flows to little lakes that drain in the narrow reach. You could connect these with an ordinary canal.

Either of these would enable people and goods to be transported by boat from coast to coast.