Possible Reasons:
* Shifting Focus: Each stanza focuses on a different aspect of the poem's central theme: loneliness and isolation. The first stanza describes the physical landscape of the Canadian Shield, the second explores the historical and cultural context of Canada, and the third reflects on the personal and emotional experience of isolation.
* Building Tension: The three stanzas can be seen as building towards a climax. The first stanza sets a somber tone, the second introduces a sense of historical weight, and the third culminates in a deeply personal reflection on loneliness.
* Formal Structure: The three-stanza structure allows for a clear, concise presentation of the poem's ideas. This formal structure also mirrors the simplicity of the landscape described in the poem.
* Symbolism: The three stanzas could represent different stages in the speaker's journey of self-discovery and acceptance of their isolation.
Ultimately, the division into three stanzas enhances the poem's impact and allows for a nuanced exploration of its central themes. The poem's structure is not simply a random choice; it contributes to its meaning and effectiveness.
It's important to note: There's no single, definitive answer to this question. The best interpretation may depend on your own reading of the poem and your understanding of its context.