In general, irony depends on oppositional or paradoxical language or situations.
For example, in The Wars, you might say the killing of the bunny rabbits is ironic. It’s ironic because, compared to what Robert will soon face, it seems rather small or insignificant. You could say it's ironic—paradoxical, contradictory, conflicting, and so on—that the killing of the small number of bunny rabbits pushes Robert into a war that killed people by the millions.
The irony of the rabbits might be Timothy Findley’s way of addressing larger ideas about death and destruction. Perhaps it’s his way of noting how widespread death and destruction can sometimes start with a relatively minor incident. According to most historians, World War One was kickstarted by the killing of one person: Archduke Franz Ferdinand of Austria.
As for “The Loons,” the irony might come from Piquette’s not so pleasant experience at Vanessa’s cottage. She’s supposed to be resting her leg. Instead, she’s pestered by Vanessa and serves as something of a helper to Vanessa’s mom.
The irony in Margaret Laurence’s story might be a way to challenge stereotypes about indigenous people. It might also be a way to contest the idea of "the white man’s burden."