The stretch of the Ayeyarwady River (aka Irrawaddy River) north of Mandalay is much less frequently explored by foreigners than the route to Bagan. Although the scenery is no more spectacular than on the Bagan run, other than in the brief “second defile” (a narrowing of the river) between Bhamo and Katha, it’s more rewarding for the scope it offers for interacting with local people. The route can also provide access to rarely visited villages: in addition to places listed in the Northern Myanmar section, boats typically stop at Shwegu (between Bhamo and Katha) and Kyaukmyaung (between Katha and Mandalay), both of which have simple guesthouses.
The government has closed the river north of Bhamo to foreigners. Since you also aren’t allowed to get to Bhamo by road, the easiest way to do the whole available route is to fly into Bhamo then take the boat south; the cheapest is to take a train to Katha (via Naba), travel upriver to Bhamo by boat, and then take the boat south again. Upriver travel is, of course, slower than downriver and all travel times depend on the season, particularly on long journeys that run overnight.