In the foreward Brown mentions
"several people have asked me if Hergé influenced the artwork in Louis Riel. I love Hergé -- his Tintin books have probably affected my drawing-style to some degree -- but my main visual inspiration here was Harold Gray's work on Little Orphan Annie. I hesitate to acknowledge this because I'm well aware that my scratchings fall far short of the beauty of Gray's imagery."
I have to say that while I was reading the book I found many visual echoes of Gray's style, but rather than being distracting it enhanced the work. Like "Louis Riel", the Annie story lines focus on personal responsibility, pitching in with help when it's needed, and fighting for the underdog. The Tintin stories have some of these aspects, but he isn't usually the underdog in a fight.
Curiously, my son thought Louis Riel looked a lot like the Tintin artwork. I figured this was because he hadn't read "Little Orphan Annie," especially the earlier stories. So, here's a comparison of some panels from Chester Brown's work "Louis Riel," and some 1941 Sunday panels from Harold Gray's "Little Orphan Annie." (One more unintended similarity: their names are both colors.)
Both Gray and Brown use a lot of Chiaroscuro and cross-hatching to emphasize the characters. In the Sunday comics "Annie" was in color, while it ran in black and white in the dailies. Nevertheless, in the panel below you can see in this excerpt that the color is almost monotone with an emphasis on dark and light. Also, compare the way both artists use the dark and light. In Brown's case Riel is literally in the dark, wondering whether the Canadian government will provide amnesty for the Metis freedom fighters, while the priest is enlightened. In Annie's case, she stays in the dark as an observer while the war profiteer gets a poke in the nose from a father whose one son was killed at Pearl Harbor, and the other is fighting with the Rangers. Gray shines the light on justice served -- the war shouldn't be about making money. Contrast this with Tintin, which rarely uses crosshatching.
In a number of places Brown uses a solid black background both to imply space, but also to give a feeling of solitude or isolation. Riel's trial, for example, takes up most of the fourth act of the book and is entirely set in a solid black background. Brown mentions this in his notes: "The black backgrounds that I've used here might give the impression of a spacious room. The court-room was actually very tiny and very crowded." But, the way it's framed gives a feeling of Riel standing alone against the law process of the Canadian government.
Gray uses the black background in a similar way. The doctor has done all he can for Annie and even his medicine is no longer working for her. He's cut off from helping her through her pneumonia, and it's up to Annie now to survive on her own.
Hergé, by contrast, only occasionally uses a black background, and that is usually in the context of a night sky, or if the lights are out.
All three artists have a similar style in drawing their characters. Gray's empty eyeballs are slightly larger than those of Brown or Hergé. I'd have to say Brown's noses are drawn more like the characters in "Little Orphan Annie" than Tintin. Hergé usually keeps his people anatomically proportional, barely stretching the natural shapes of the human body. Both Gray and Brown, however, distort their characters, giving them massive girths, stretched faces, and imposing hands.
And finally, the most compelling comparison between the two artists is their consistent use of two-point perspective. The camera angle, raised to a slightly aerial position and to the left, not only gives a documentary feel to the art, but also seems to suggest a higher moral view. Hergé often used the two-point perspective, but his camera is usually level with the characters, bringing the reader into the story as if it were a newsreel. When Brown raises the camera to this aerial view it somehow manages to be both omniscient, and to say to the reader: "look, this is what's happening. Can you believe it?" It's as if he's removing us from the action to give us a chance to judge the characters.