  The formation process of fossil groups (FGs) is still under debate, and large
samples of such objects are still missing. The aim of this paper is to increase
the sample of known FGs, and to analyse the properties of their brightest group
galaxies (BGG) and compare them with a control sample of non-FG BGGs. Based on
the Tinker spectroscopic catalogue of haloes and galaxies, we extract 87 FG and
100 non-FG candidates. For all the objects with data available in UNIONS in the
u and r bands, and/or in an extra r-band processed to preserve all low surface
brightness features (rLSB), we made a 2D photometric fit of the BGG with GALFIT
with one or two Sersic components and analysed how the subtraction of
intracluster light contribution modifies the BGG properties. From the SDSS
spectra available for the BGGs of 65 FGs and 82 non-FGs, we extracted the
properties of their stellar populations with Firefly. We also investigated the
origin of the emission lines in a nearby FG, NGC 4104, that has an AGN. A
single Sersic profile can fit most objects in the u band, while two Sersics are
needed in the r and rLSB bands, both for FGs and non-FGs. Non-FG BGGs cover a
larger range of Sersic index. FG BGGs follow the Kormendy relation derived for
almost one thousand brightest cluster galaxies (BCGs) by Chu et al. (2022)
while non-FGs BGGs are mostly located below this relation, suggesting that FG
BGGs have evolved similarly to BCGs, while non-FG BGGs have evolved
differently. The above properties can be strongly modified by the subtraction
of intracluster light contribution. The stellar populations of FG and non-FG
BGGs do not differ significantly. Our results suggest FG and non-FG BGGs have
had different formation histories, but it is not possible to trace differences
in their stellar populations or large scale distributions.
