One key goal of the {\it Hubble Space Telescope} Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey is to track galaxy evolution back to $z\approx 8$. Its two-tiered "wide and deep" strategy bridges significant gaps in existing near-infrared surveys. Here we report on $z\approx 8$ galaxy candidates selected as F105W-band dropouts in one of its deep fields, which covers $\sim 62.9$ arcmin$^2$ to 4 ks per filter depth in the Great Observatories Origins Deep Survey southern field. We construct two independent samples using different but legitimate photometry and procedure. While they differ significantly on an object-by-object basis, our conclusions based on these two samples are similar. Two of our candidates have $J<26.2$ mag, and are $> 1$ mag brighter than any previously known F105W-dropouts. We derive constraints on the bright-end of the rest-frame ultraviolet luminosity function of galaxies at $z\approx 8$, and show that the number density of such very bright objects is higher than expected from the previous Schechter luminosity function estimates at this redshift. Another two candidates are securely detected in {\it Spitzer} Infrared Array Camera images. These are the first such detections at $z\approx 8$. Their derived stellar masses are on the order of a few $\times 10^9$ $M_\odot$, from which we obtain the first measurement of the high-mass end of the galaxy stellar mass function at $z\approx 8$. The high number density of very luminous and very massive galaxies at $z\approx 8$, if real, could imply a large stellar-to-halo mass ratio and an efficient conversion of baryons to stars at such an early time.