It was originally decided [1] that calling addHitRegion() should update the location information for the fallback element with the location of its corresponding hit region:

> RS: updating location information in Accessibility APIs
>
> <richardschwerdtfeger> Updating the accessibility API of the
> location of fallback elements that are representative of the
> corresponding hit region location.

However, this text was never added to the spec.  The oversight was pointed out and discussed here [2]

I propose the following step be added after step 12 in addHitRegion() [3]

13. If the arguments object's control member is not null, inform the user of the location of the region representing the control given by the control member's value for this canvas element, if any. The full location of the corresponding fallback element, pertaining to the control, as represented by the region is passed to the accessibility API, if supported. 

Optionally, we could add non-normative text similar to that which is included with drawFocusIfNeeded():

Note: "Inform the user", as used in this section, could mean calling a system accessibility API, which would notify assistive technologies such as magnification tools. The methods above allow the user agent to report the bounding box of the path as the bounds of the element passed as an argument.

[1] http://lists.w3.org/Archives/Public/public-canvas-api/2014AprJun/0039.html
[2] http://lists.w3.org/Archives/Public/public-canvas-api/2014JulSep/0033.html
[3] http://www.w3.org/TR/2dcontext/#dom-context-2d-addhitregion