Upvote:-1
The main route would be: Venice, [Mountain crossings], Vienna, Stockerau (north bank of the Danube outside of Vienna), Prague, [Mountain crossing Pass am Geiersberg], Dresden.
These would have been long established trade routes.
No major waterways along the way in 1700.
From Prague, the river Moldau flows north into the Elbe and from there on to Dresden.
Serious planning for a Donau/Moldau/Elbe connection only started in the early 19th century. Most references about the shipping on the Elbe (north of Dresden towards Hamburg) is about the shipping of goods.
Sources:
Upvote:-1
Working from the map posted by @Jan, the route would be:
Depart Venice to Laubach (optionally Klagenfurt via Burgo and Brixen);
The route through Klagenfurt would be inhospitable in winter, but perhaps more scenic in summer.
Depart Laubach for Vienna, via Gratz and Loeben (meeting up with any travelers through Klagenfurt);
Depart Vienna for Linz;
Linz is the only Danube crossing between Vienna itself and Passau. Crossing at Vienna takes one into Moravia through Olmutz (ie Austerlitz) and then into Silesia via Breslau - a very roundabout route, but possible.
Depart Linz for Prague;
Shortly after leaving Linz one descends into the Moldau/Vitava river valley, which flows into the Elbe at Prague. This stretch has only ever been intermittently navigable, so travel would have been on foot, horseback, or carriage.
Depart Prague for Dresden;
One is now simply following the Elbe river valley. The Elbe has always been navigable by commercial vessels as far inland as Prague, according to Wikipedia, so this could be a comfortable downstream river excursion.
Upvote:2
Here is a roughly contemporary map (from 1727) with postal routes that includes both Venice and Dresden. This does not yet mean your character would actually take any of these routes (e.g. because there were cheaper modes of transportation?) but it might be a start.
Please note that according to the map legend, routes drawn with a single line are for post riders ("reitende Posten") and routes drawn with duplicate lines are for coaches, carts or the like ("fahrende Posten").