As long as you let him know that movies are not exactly accurate (in terms of story, what really happened, what you see, equipment used etc), I would say that most movies from before the 90s are PG enough.
The big budget 'A Bridge Too Far' details Operation Market Garden. It presents the story of the operation through American, British, and Polish characters. It is not exactly historically accurate, but would be a dramatic way of beginning ones learning about the operation. As far as I recall, there is not much in the way of gore in the movie. For a perhaps more accurate cinematic version of the operation, there is the British movie 'Theirs is the Glory', a reenactment of the fighting at Arnhem filmed on location and with surviving British paratroopers. Some poor acting, but a bit more accurate than the former. As far as I recall, no gore. If you have Netflix, the latter is available on there.
'The Longest Day', covers the invasion of Normandy from American, British, and French perspectives (I don't recall their being Canadian troops shown). It is an all star, black and white, treatment of 6 June. Problems with accuracy yes, but provides a dramatic, non-gory take on what happened.
'The Battle of Britain' is a largely ungory film (I think there is a scene or two were you see people starting to get burnt in planes, but I am not 100 per cent sure since it has been a long while since I have seen it.), showing the 1940 aerial battle between Germany and the United Kingdom.
'Tora! Tora! Tora!' is an excellent American-Japanese movie about the Battle of Midway. I do not recall there being gore in that either.
If he can stand subtitles, 'Das Boot' is a German movie about their submarine force. It is a pretty long one, but fairly entertaining look at the German U-Boats. In the same manner, there is an excellent movie from a few years ago called 'Downfall'. It is the story of the final few days in Hitler's bunker during the Battle of Berlin at the end of the war. It is the story of Hitler and his secretary's. It is not gory in the slightest, and it provides the valuable lesson that Hitler was human after all. It does not show him sympathetically nor is it neo-Nazi, so you don't have to worry about things like that. It shows him as the frail, pathetic, angry person he was, but not some sort of ungodly monster.
I would suggest avoiding the big-budget and famous movie 'The Battle of the Bulge', while it is not gory, it completely screws up telling the story of what happened. It makes stuff up, and iirc was filmed in Spain with what looks like desert like terrain when it is suppose to be depicting the snow covered Ardennes forest. Likewise, I recall seeing numerous movies showing the British fighting in the Desert, while entertaining, most were bunk when it comes to historical accuracy.
For a more lighter take on the war, there is always the 'Dirty Dozen' and 'Kelly's Heroes'. Good movies, no gore, all fictitious.
For a more documentary approach, I would highly recommend 'The World at War' series. It covers the entire war, utilizing period footage. It walks the viewer through the German invasions of Poland and Western Europe, the Battle of Britain, the naval fighting, the Eastern Front, the Pacific, Normandy, the fall of the Reich, and the Holocaust. I do not recall it using any gory footage, and considering your son's appetite to learn about the subject, this 26-part series will probably do him more good than war movies.
In the same light, there are usually all sorts of documentaries on tv and cable talking about the war. Some are good, some are rubbish. As Tim as noted, there is an abundance of WW2 footage on Youtube. However, one should caution that a good chunk is propaganda footage. So while you son would see tanks and troops and what not, it may not be beneficial from a learning point of view. There have also been neo-Nazi documentaries uploaded onto the site that will - if seen - distort rather than teach.
As for books, I recall that David Glantz is one of the leading historians on the Eastern Front. I have not read his works, so I do not know if they are overly academic and perhaps a bit over the head of an 8-year old. If you can find them in the library, you should give them a look over. Anthony Beevor has released two easy to read books on the Eastern Front: 'Stalingrad' and 'Berlin: The Downfall 1945'. They are popular histories, in other words easy to read and lacking the academic approach. The latter, however, covers the Soviet atrocities of mass rape following the capture of Berlin.
Finally, you could check out Osprey Publishing. Their books are short treatments on various battles, campaigns, and armies. They are also well illustrated with maps, diagrams, and photos. The books called 'x vs x' usually provide various information about the plane or tank involved, and then an example or two of battles were each weapon system met. They have an online catalogue here: http://www.ospreypublishing.com/world_war_2/ While they are not always highly rated and sometimes way to short, they would seem to be highly recommended for your son's age. Local libraries should have some, and they can usually be bought for second hand cheaper on amazon.