> I suspect the Edwardian suit had a slippery inner lining (or maybe cotton inner lining) but no canvas structural lining in between.

This varied like everything in the period. My Edwardian recreation is a single layer. There's no structural canvas.

I'm not entirely sure when structural interfacing became common in virtually all mens' suit jackets, but based on my personal experience wearing recreations and going down the rabbit hole of late Victorian & early Edwardian clothing... I tend to view structural interfacing as something typical of more formal wear as opposed something you would see in everyday wear. So it's kind of a more modern evolution of the mens' formal suit that we always see it. I.e: historically you probably would have seen interfacing in tuxedos and tails and would have been less likely to see it in every day business and work attire.

Historically structure is something that has been achieved just as much through different undergarments and pieces (think of a 18th century pennier for example), rather than "one size fits all, off the shelf" clothing that is so common today that is going to include everything in one piece.

Structure in general has been insanely common throughout history. Both mens' and womens' clothing often featured structural boning, for example. I also mentioned penniers above. Victorian women's wear then mostly dispensed with penniers and women started padding their rear-ends, because "baby got back" was all the rage then too.

So most of the Victorian woman's hourglass figure, that we assume was created through unhealthy tight lacing that tried to squish and conform the woman's waist into something that it wasn't, was actually more commonly created by padding out areas around the waist (the hips, rear-end, bust and shoulders - you can't have Victorian fashion without puff sleeves) to create a certain proportion. It was a magic trick. You have to remember that people wore corsets and stays as undergarments for hundreds of years as everyday wear. This stuff was way way way more comfortable than we imagine. In fact, I think we tend to project a lot of our modern clothing trends onto the past and assume that if WE'RE uncomfortable in what we see as "formal wear", that people of the time must have been as well. Tight lacing corsets and trying to strong-arm the human body into a particular shape is something that is actually more modern than we tend to assume.

Also what we consider to be "formal wear" today is different than formal wear of the past. So formal suits may have had structural interfacing, but men also wore corsets (yes mens' corsets were common, but also remember that corsets were undergarments and wearing them as outergarments is a very modern trend that would have made Victorians blush) and other forms of undergarments that could create an outer figure through padding and shaping.

So I'm inclined to suspect that my Edwardian suit, which was made to be a historic recreation, is likely the most common. It looks formal to our modern eye, but was intended to be worn as every day business attire and so there is no structural interfacing.

But if you come across something like a tuxedo with tails of the era, I would imagine that would be more likely to contain structural interfacing as well as stays (small bones intended to stiffen and provide structure to a particular part of the garment).