As is ever the case - looking for a more specific entry one finds a useful source of reference which (in this case) has hardly been perused.
(Updated Oct 18)http://heritage.canadiana.ca/view/oocihm.lac_mikan_133700
Although a Canadian source there are many entries for 21 Army Group and for unit and formations attached to Cdn Groups,
Enjoy and if possible use any info gleaned to update records on this site.
"The War Diaries posted are from LAC files, and digitized by Heritage Canadiana and are free to use by all.
Please note that many of these files contain, not only War diaries, but Operational Orders, Messages, Part 1 Orders, strength reports and many other documents that were stored in the boxed files.
The information is NOT necesssarily in any particular order, so records (such as War Diaries) are interspersed throughout the reels, ie more than 1 unit may feature on a reel of 1400 plus pages, and the files may NOT be in year order. In order to look for information you may have to read an entire Reel or series of Reels.
The Information on Canadiana's site only list the REEL Number, and in order to find out what is on a reel, you have to open it, and look for the index (which is found "somewhere" with the first 20 pages, each reel is different) Fortunately in your browser line you an alter the reel number and page number to speed through files.
The War Diary Files in this thread have been identified by reading the index in the Canadiana File. So hopefully the Units you are looking for can be easily found.
EXAMPLE: War Diaries 4th Medium Regiment, RCA
The digitizing of the files is a LONG, LONG, PROCESS, so the files presented here, are what has been completed by Canadiana. Files will be added to this site, as more information becomes available
We hope this helps your research....................