Several attempts to download & install the World Update XI: Canada have failed. 5.21 GIBs are indicated as partially installed from a total of 6.29 GIBs, with the installation stopping each time at "decompressing microsoft-airport-cyfb-iqualuit-0.9.3fspackage." The download/install just stops there and never proceeds further. I've cancelled the download and retried several times to no avail. On occasions the program crashes-to-desktop and I restart the program in "safe mode" but that makes no difference. This is Steam MSFS.

Any suggestions short of a total reload?

Sure. Pause the sim while the file is being decompressed. Pay attention to the exact name of the file being decompressed. Search for that file name (i.e. find the folder it is in). 

Go to that folder. Delete that file. Put all the other files in the folder in order by date/time. Delete the file that was downloaded right before this last file. 

It may be that the folder where the file is located does not hold all the previous files that were downloaded. In other word there might be one folder into which files being downloaded to be decompress in are stored. And another folder where the decompressed files are moved to right after decompression.. You may have to go to this second folder to find the previous downloaded file. But find it and delete it too.

Quit MSFS and then reboot it. 

The above procedure has worked for me. I'm not the first to use it. I learned about it right here, a long time ago in this forum. 

I found the file in question in my Steam folder. I moved it to another drive for safe keeping and then rebooted MSFS. This time it started the download with the file that had originally "stuck" but completed the decompression and downloaded the rest of the update. Thanks for pointing me it the right direction.