I've found a few good resources for map tiles.
The CRD takes aerial photos every two years and makes them available as WMS layers. Add 2015 to an OL4 map:

//CRD
        layerCRD = new ol.layer.Tile({
          //extent: extent,
          source: new ol.source.TileWMS({
            url: 'https://mapservices.crd.bc.ca/arcgis/services/Ortho2015/MapServer/WMSserver',
            //crossOrigin: 'anonymous',
            params: {
              'LAYERS': '5',
              'FORMAT': 'image/png',
              'SRS': 'EPSG:3857'
            },
            serverType: 'mapserver'
          })
        });

The BC Government also provides aerial/satelite tiles

layerBCWMS = new ol.layer.Tile({
          //extent: extent,
          source: new ol.source.TileWMS({
            url: 'https://openmaps.gov.bc.ca/lzt/ows/',
            crossOrigin: 'anonymous',
            params: {
              'LAYERS': '140',
              'FORMAT': 'image/png',
              'SRS': 'EPSG:3857'
            },
            serverType: 'mapserver'
          })
        });

and map tiles, too

layerBC = new ol.layer.Tile({
          source: new ol.source.XYZ({
            url: 'http://maps.gov.bc.ca/arcgis/rest/services/province/web_mercator_cache/MapServer/tile/{z}/{y}/{x}',
            numZoomLevels: 18,
            maxZoom: 17
          })
        });

Licensing is (as of October 2017) quite liberal.