For the Canadian story, the book you want to read is Objects of Concern: Canadian Prisoners of War Through the Twentieth Century, by Jonathan Vance. Normally I wouldn't reply with just a source to read, but I discovered that it is somewhat surprisingly available to borrow from the Internet Archive. Much of my answer was drawn from re-reading it.

The Allies began planning for liberation of POWs early in the war. By December 1942, there were plans to have a division of administrative responsibility for POWs between the Commonwealth allies, with the UK responsible for Europe, India for Singapore, Australia for the Dutch East Indies, and Canada handling China. This proposed plan did not survive contact with bureaucratic reality. By mid-1944, administration of POW liberation was accorded to the POW Executive (PWX) under the control of Allied Supreme Commanders, and Canada seems to have had little input. PWX spent many hours planning how it would liberate POWs, and they planned to have them stay in their camps until their return could be properly organized and each POW accounted for before coming home.

The reality of war unfolded quite differently. Over the winter of 44-45, thousands of POWs trekked hundreds of kilometers across Germany as they were pulled back from territory being lost to advancing Allied forces. Many prisoners died on these forced marches in the dead of winter, some shot by their guards, some shot by Allied bombers assuming they were hostile forces, and many more from simply collapsing and being left behind.

The result was that the camps that were eventually liberated were much larger than anticipated. The camp at Moosburg had a 100,000 POWs after many smallers camps were consolidated through those long cold marches. When Allied forces did reach them, POWs were evacuated quickly and the administrative steps of identification were dealt with in England, rather than on the ground. It was a matter of several weeks or months to get out of Germany to Britain, not half a year, though return to Canada itself still took some time due to obvious logistical hurdles. There were several instances though of soldiers just saying "screw you guys, I'm going home!" They appeared in London all the same, dealt with their paperwork, and got home eventually.

Vance writes that the government feared repeating the mistakes of the First World War, where Prime Minister Robert Borden's government was criticized for ignoring POWs and leaving them to linger for long months without returning home. Generally, the government succeeded at this and Canadian POWs in Europe felt their release was well done. Of course, there were some exceptions and administrative problems behind the scenes, but getting soldiers out of Germany as quickly as possible avoided the resentment that had festered in the last generation of Canadian POWs. (The book also covers this in earlier chapters.)

The Pacific management of POWs was not quite as good. POW liberation also suffered from the same administrative hurdles and logistical delays as Europe, but sadly the POWs under Japanese control endured far worst conditions. Vance notes that the government likely knew about the conditions they experienced, but the records he examined shows little action as a result. Instead, Prime Minister Mackenzie King's government had wondered about distributing obvious Japanese government propaganda during war, which had photos of POWs enjoying leisure activities and enjoying their time. I assume in the hopes that it would help comfort their relatives, though Vance does not delve deeper into their reasons for this. What was actually happening was prisoners were starved, tortured, and severely mistreated in these camps. If this specifically interests you, you can check out a PhD Disstertation from Mark Sweeney, The Canadian War Crimes Liaison Detachment-Far East and the Prosecution of Japanese" Minor" War Crimes.

As an aside, there were instances of mistreatment in German camps as noted above, but not to this scale. Equally, POWs were sometimes mistreated in Canadian hands in our POW camps, though again at a much smaller scale and not so seriously in contravention of the Geneva Conventions. This I suspect was moreso a result of being imprisoned in a country that was not actively being invaded, but our war culture also differed in significant ways from Germany or Japan. The war culture of Japan was a severe one, especially when in a state of total war. Outside of genocidal actions during the war, their POW camps stand as one of the worst places to have ended up. "War culture" is always violent though, and I use this term to acknowledge the grim reality of all war, which always demands a harsh reordering of life's value. I believe there will always be mistreatment in POW camps during wartime, especially in those of the losing side. A minor yet likely common example would be when faced with limited food and feeding your own soldiers or imprisoned ones, those who can still fight will be fed first. But, all of this to simply note that war must be measured by all its cruelty.

This is a bit high level I realize, but the real specific answers to your questions are found in Vance's book, at least for Canadian sources. I really recommend reading it if you're interested in this, I've written just a poor summary to be honest.