Below is a recommended list of data portals by provider where various national geospatial data can be free downloaded. Think about which government organizations might have created the data you are looking for, and start with their website's search box.
Agriculture and Agri-Food Canada
- Agri-Geomatics (AAFC): provides geographic-based information and knowledge to improve decision making and risk management for agriculture and the environment. Various geospatial data dealing with land, soil, water, climate and biodiversity resources in Canada available for download.
- CanSIS - Canadian Soil Information System (AAFC) manages and provides access to soil and land resource information on behalf of the federal, provincial, and territorial governments.
Natural Resources Canada
- Atlas of Canada: provides a comprehensive collection of maps (at 1: 2 million, 1: 7.5 million scales) and related information about Canada’s environment, people & society, economy, history, climate change, freshwater, health and topography (Toporama). GIS files for some of these topics can be downloaded following the link called "Read about this map".
- Geographical Names of Canada: provides access to nearly 350,000 currently approved geographical names stored on the Canadian Geographical Names Database.
- GeoGratis: a wealth of vector/raster/tabular data distributed by Nature Resources Canada.
- GeoScan: bibliographic database for scientific publications of the Earth Sciences Sector (ESS) of Natural Resources Canada. A series of Canada topographic maps are available for download.
- Geoscience Data Respository: a collection of Earth Science Sector geoscience database, including geoscience map, geophysical survey and data regarding geochemistry, energy, minerals, marine etc.
- Water Survey of Canada: provides various HYDAT and real-time hydrometric data for Canada (more info)
- Census Geography (Statistics Canada): provides access to information on a wide range of census geographic areas (from provinces and territories down to city blocks) which allows users to relate census data to them
- GeoBase: seamless Canadian data including administrative boundaries, digital elevation data, geodetic network, geographic names, land cover, national hydro network, national road network and satellite imagery.
- GeoConnections Discovery Portal: one-stop web access to Canadian geospatial datasets. It allows you to search for a wide variety of data by subject and location.
- Geography Network: ESRI Canada's portal for finding and sharing Canadian geographic content, including maps and data from many of the country’s leading providers.
- Open Data Pilot Project: source for open data released by the Canadian federal government
- Great Lakes Environmental Research Laboratory (GLERL) includes data that covers physical properties, hydrology, hydraulics, meteorology, ice and snow data, biological aspects, chemical and sediments data, waves and circulation data, and lake levels.
- Great Lakes Information Network (GLIN): provides a wide range of geospatial data related to the environment, economy, and tourism of the Great Lakes region.
- National Forest Database: provides various information on the forest resources of Canada including forest inventory, wood supply, forest fires and forest insects etc.
- Fisheries and Oceans Canada Interactive Maps: provides access to several maps and GIS data regarding the ocean and fishes resources of Canada.
- Maps, Plans and Charts of Canada from Library and Archives Canada provides item-level descriptions on approximately 40,000 maps, plans, charts and drawings.