When two or more flows are selected, the canvas displays a tile for each flow. A tile is a scaled-down version of the flow design similar to a thumbnail. Tiles can't be edited. However you can select a particular tile and edit its flow properties in the Properties pane.
In tile mode the canvas never shows horizontal scroll bars. Instead the size of the tiles is adjusted so that a predefined number of tiles fit on a row. The maximum number of tiles shown can be set as well.
Double click the tile in the canvas; or
Select the tile in the canvas and choose the "Show at full size" menu item in the canvas context menu; or
Select the flow in the Flows pane (without selecting any other flows).