See this adobe tutorial to know multi-Artboard: http://www.adobe.com/designcenter/illustrator/articles/lrvid4016_ai.html
Multicanvas solution is not the same as pages and can't follow the SVG pageSet spec. The multicanvas, as the multi-artboard, can (frequently must) have different sizes and can be freely placed on the 2D space. A canvas may overlap a part other canvas.
Each canvas can be printed independently and that feature helps to unify the art conception for the most applications of an art project.
The multicanvas feature may be incompatible with the multipage feature, so, the user may chose the working mode on the "document properties" dialog. The default must be multipage and that will show the page tabs on the interface and the "new page" button, when selecting multicanvas that will show the canvas controls and the "new canvas" button.
More about Inkscape multipage plan: http://wiki.inkscape.org/wiki/index.php/Multipage
additional related links:
Blueprint "Multiple pages support"
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Bug #170369 “Multiple Pages Support - SVG 1.2 Compliance”
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