A route I can suggest is biking along the canal – Damse Vaart – to Damme. Further along the canal (after crossing two canals) turn left over the bridge for a detour to Oostkerke. You can backtrack to the canal, but also turn halfway left following the winding Krinkeldijk at the northside of Damse Vaart. Continue further to Sluis in the Netherlands, Sint Anna Ter Muiden is worth a detour there. From the latter through the “polder” = countryside to mainroad N657 just north of Sluis.
Soon you can turn left to Retranchement just before the canal, more scenic is the road 1 km further. Continue further to Het Zwin, a former sea inlet and now a nature reserve. From there you can decide going further in the Netherlands or go west along narrow paths to the dunes east of Knokke. From the latter you can train back to Bruges. Want to note that they are extending Het Zwin and hard to say you can make use now of the bike path at the southside there. Otherwise you have to go directly from Retranchement to Knokke.
Total distance about 35km and be aware wind can be strong so close to the coast, in this case an electric bike can make the trip more convenient.
Biking to De Haan is an option too, but the countryside is less scenic to my opinion. But you can rent bikes there as well as in many other places along the coast.