Guadalcanal is the name of an island in the south-western Pacific that was the site of a famous World War 2 battle. The name comes originally from Spanish as it was named (or renamed) by Álvaro de Mendaña de Neira. The name is pronounced (using the International Phonetic Alphabet) as /ˌɡwɑːdəlkəˈnæl/. Guadalcanal has four syllables with the stress on the final syllable, the first syllable is the secondary stress. This results in something like Gwa-del-ca-NAL.
If you want to learn more about the International Phonetic Alphabet, you can find a guide here: International Phonetic Alphabet and Phonemic Alphabets