We have analyzed the hourly cloudiness record at 103 Canadian stations where observations were made by human observers. The records at 56 stations span the period from January 1953 to April 2003, while the remaining 47 stations have shorter (35-49 years) records. All records are nearly complete. Our assessment of cloudiness changes in the last half century was preceded by an intensive assessment of observational biases. This assessment involved statistical change point analyses, station metadata analysis and visual inspection with a time series visualization tool. Changes in observer training and observing practices (seven versions of Canadian Manual of Surface Weather Observations (MANOBS) have been published so far), frequent observers changes, etc. were found to introduce significant step-changes in cloudiness time series, especially in the period before the latest version of MANOBS was published in January 1977. We carried out the analyses for each of the 11 cloudiness conditions/categories (from clear sky to overcast: 0/10 - 10/10) separately, while preserving consistency among the 11 categories. Significant trends and low-frequency oscillatory variability were found after removing the effect of observational biases.